1. Field of the Invention
The present invention relates to a set of an ink and a reaction liquid, and an image forming method.
2. Description of the Related Art
A method for forming an image by providing another liquid for making the image good than an ink containing a coloring material as what is called a reaction liquid and applying the reaction liquid and the ink to a recording medium has heretofore been variously proposed as an ink jet recording method. According to this method, aggregation of the coloring material in the recording medium is accelerated by the reaction liquid, whereby the performance of the image can be improved compared with a method for forming an image with an ink alone.
For example, there has been a proposal for controlling an ink and a reaction liquid so as to slow the speeds of penetration and diffusion thereof into a recording medium, not by improving the reactivity between them, thereby achieving a high optical density (see Japanese Patent Application Laid-Open No. 2008-308662). Specifically, a reaction liquid whose dynamic surface tension at a lifetime of 30 milliseconds is 41 mN/m or more and an ink whose static surface tension is high to some extent are used, thereby ensuring a time period during which a coloring material aggregates on the surface of the recording medium to improve the optical density. On the other hand, there has been a proposal that a first ink containing a pH-sensitive resin are brought into contact with a second ink having a predetermined pH to insolubilize the pH-sensitive resin, thereby suppressing the feathering of an image (see Japanese Patent Application Laid-Open No. 2000-129184).